Conventionally, a navigation apparatus for use in a vehicle provides a route guidance and the like for a driver of the vehicle or the like based on road map data. For example, the navigation apparatus provides a route guidance from a start point of a travel to a destination when the start point and the destination are input.
The navigation apparatus uses as the road map data, for example, a road map as well as road information such as a road type (e.g., a national road, a prefectural road and the like), a road number, a road name (e.g., route 1, a causeway or the like) and the like. The road map data is stored in the navigation apparatus. Further, when the vehicle approaches a branch point in a route to the destination, the navigation apparatus displays on a screen of a display unit the road information of the road that comes after the branch point. In addition, the road information is stored in association with each of the branch point (i.e., a node) as disclosed in Japanese patent document JP-A-2002-286487.
However, the disclosure of the above patent document displays the road information of the road on which the vehicle travels after passing the approaching branch point, without displaying the road information of the road that lies ahead of the road to be traveled just after passing the approaching branch point.
On the other hand, by storing the road information of the road that is adjacent to the approaching branch point with a method that pre-reads the road information of every branching road from the approaching branch point, the road information of a navigation route can be displayed when the vehicle approaches the branch point.
However, when the navigation apparatus is configured in an above-described manner, the branch road that further branches ahead produces plural combination of roads, thereby leading to storage of the road information of all those road combinations and also leading to a display of all of the stored road information on the screen.
Therefore, when the navigation route consists of the branch road that further branches ahead to have plural roads in the traveling direction, the road information of all those roads is displayed on the screen, thereby making the size of the road information (e.g., character and/or illustration of road name/road number) smaller on the screen, or displaying the road information that is irrelevant to the navigation route.
In that case, the pre-read and stored road information may be selectively displayed on the screen in a manner that chooses and displays appropriate road information only (e.g., the road information of the road that consists of the navigation route). However, the method to select the appropriate road information has not been conceived to date.